Swell Alert: Long S groundswell Inbound across the East Coast

22 May 2018 2 Share

Ben Macartney

Chief Surf Forecaster

COASTALWATCH PLUS EXCLUSIVE | SWELL ALERT

Issued Thursday May 22, 2018

This week’s brilliant autumn run of all-day offshores, sunshine and small-scale S swell belies a major upswing in wave energy across the NSW coast over the next few days. Indeed you could say the warm, sunny weather currently in place over the coast belie the development of several deep lows inside our swell window, south of Tasmania this week. Even as I write, the first of these storms is churning out a 40 knot WSW fetch across the southern Tasman Sea – and this in turn leads in a highly active phase in S groundswell inbound across the region from Wednesday onwards.

A powerful spike in long-period energy is set to rock the NSW coast under favourable offshore winds on Wednesday. Photo: Dan Bielich.

A powerful spike in long-period energy is set to rock the NSW coast under favourable offshore winds on Wednesday. Photo: Dan Bielich.

In Summary:


  • A first, long-period pulse of S groundswell peaks across Sydney, Newcastle and the South Coast on Wednesday morning, generating large sets ranging from 5 to 8ft across south facing beaches, with scope for larger 8 to 10ft+ sets on offshore reefs and across Newcastle and Hunter coasts.

  • Early light WSW winds see excellent conditions along open beaches as the swell wraps at anywhere from 3 to 6ft+ depending on exposure.

  • The groundswell eases notably as winds tend light and variable during the afternoon.

  • The groundswell builds across the Mid North Coast throughout the day, showing peak size during the afternoon.

  • Across far northern NSW the groundswell builds in late, peaks overnight and holds solid size in the 4 to 6ft plus range on Thursday morning.

  • The groundswell wraps into southern Queensland at lower 2 to 4ft levels along exposed areas, while grading much smaller inside the points and bays.

  • A second smaller, but still powerful pulse of S groundswell is projected to reinforce surf heights state-wide on Friday and Saturday.

Overview
A succession of deep frontal lows sweeping eastward below Tasmania over the past few days culminated in the development of an intense storm inside our swell window on Monday and Tuesday. The associated fetch is supported to the northwest by a strong, slow moving high pressure system that’s facilitating a both strong and extensive fetch; extending south-westward from the southern Tasman Sea, deep into the Southern Ocean below Tasmania. Although partially shadowed by Tasmania, the fetch and resulting groundswell will extend north into the Tasman Sea  over the coming days, generating powerful surf across the entire NSW coast.

This image depicts forecast surface winds, showing the deep belt of gales extending across our south swell window on Monday. Source: BOM.

This image depicts forecast surface winds, showing the deep belt of gales extending across our south swell window on Monday. Source: BOM.

As depicted below, the resulting sea-state is projected to top out at about 30ft offshore on Tuesday; spawning a long-period pulse of S groundswell that spreads radially from the source, running south to north along the NSW coast at peak intervals of 16 to 17 seconds on Wednesday and Thursday.

FOLLOW THE PROGRESSION OF THE SWELL ON THE WAVE TRACKER

A deepwater SW swell of 30ft spreads up into the Tasman Sea; generating large surf along the NSW coast on Wednesday. Source: Wave Tracker.

A deepwater SW swell of 30ft spreads up into the Tasman Sea; generating large surf along the NSW coast on Wednesday. Source: Wave Tracker.

The straight southerly direction of the groundswell will invariably translate into wide-ranging surf-heights depending on a location's exposure - so expect big disparites between less-exposed east facing beaches and offshore reefs. This event is likely to start out a little undersized as it fills in on Wednesdayacross Sydney and surrounds early before pulsing to large/ heavy levels mid-morning.

Mid and Northern NSW and Southern Queensland
The long period energy will swiftly propagate north on Wednesday to peak across mid and northern NSW coasts throughout the afternoon/ evening, before steadily scaling down again throughout Thursday. Like locations further south, this should see extra-large surf showing across southern exposures, with scope for heavy 8 to 10ft+sets on outer bombies focussing the deepwater energy.

In contrast, southern Queensland coasts will only see a fraction of the true deepwater energy wrapping in across the region; potentially generating some solid sets in the 3 to 4ft range at select locations pulling in the groundswell; but otherwise only amounting to very low 1 to 2ft plus levels along the majority of open areas as the swell shows up on Wednesday afternoon and Thursday morning.

Mid and Northern NSW and Southern Queensland
The long period energy will swiftly propagate north on Wednesday to peak across mid and northern NSW coasts throughout the afternoon/ evening, before steadily scaling down again throughout Thursday. Like locations further south, this should see extra-large surf showing across southern exposures, with scope for heavy 8 to 10ft+sets on outer bombies focussing the deepwater energy.

In contrast, southern Queensland coasts will only see a fraction of the true deepwater energy wrapping in across the region; potentially generating some solid sets in the 3 to 4ft range at select locations pulling in the groundswell; but otherwise only amounting to very low 1 to 2ft plus levels along the majority of open areas as the swell shows up on Wednesday afternoon and Thursday morning.


Second Pulse Hits on Friday and Saturday
Wednesday’s first spike in energy is the first of two S pulses. Going on latest model guidance, Wednesday’s pulse will be closely followed by another lnog S groundswell, reinforcing surf-heights state-wide on Friday and Saturday. Having said that, latest model runs tending to downplay the influence of a new low moving below Tasmania later this week, so stay tuned to the detailed forecast to keep track of how this will evolve.

Latest virtual buoy readings for Sydney show a big spike building in across the region on Wednesday morning before easing to lower levels during the afternoon.

Latest virtual buoy readings for Sydney show a big spike building in across the region on Wednesday morning before easing to lower levels during the afternoon.


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